The present invention relates to a shift operation device of an automatic transmission provided on a driving-force transmitting system of a vehicle.
As a transmission provided on a driving-force transmitting system of a vehicle, a mechanical automatic transmission is known.
The mechanical automatic transmission enables automatic gearshift by actuating an actuator to operate a gearshift mechanism and connect/disconnect a clutch. For example, as shown in FIG. 14A and FIG. 14B, a shift operation device of the automatic transmission is provided with a shift shaft 100 capable of moving in a shift direction sf and in a select direction se, shift lugs 120 formed in an outwardly protruding manner respectively on parts of shift rails 110 arrayed in parallel in the select direction se, and shift forks 131, 132, 133 integrally joined to other parts of the shift rails 110, respectively.
The shift shaft 100 is provided with a control finger (select member) 140 protruded in a radial direction, and a pair of pawl portions 121, 122 are formed at each of the shift lugs 120 with an interval in the shift direction sf.
In the above-described mechanical automatic transmission, the shift shaft 100 is moved by an actuator to arrange the control finger 140 between the pair of pawl portions 121, 122, thereby pressing and moving the pair of pawl portions 121, 122 selectively in one or the other direction of the shift direction sf. Then, the shift fork 131 working therewith shift-actuates a corresponding gear (not illustrated).
Incidentally, a dual clutch-equipped automatic transmission in which two clutches are incorporated between the above-described automatic transmission and an engine which is a driving source has been developed. This automatic transmission is provided with a first main shaft and a second main shaft, and the first and second main shafts change a rotating force coming from each of the clutches and transfer the rotating force to each of corresponding auxiliary shafts, thereby the changed rotation from each of the auxiliary shafts is transmitted to transmission output gears.
In the above-described dual clutch-equipped automatic transmission, a state in which one gear is connected to one of the clutches via the first main shaft is switched to a state in which a target gear is connected to the other of the clutches via the second main shaft. In this instance, the shift operation of the target gear is completed in advance and, thereafter, one of the clutches is disconnected. Thus, it is not necessary to be in a neutral state at the time of gearshift, and a seamless gearshift can be achieved.
A shift operation device adopted in the above-described automatic transmission is, for example, as shown in FIG. 15A, that where a current gear is a fourth speed gear, the gear is shifted to a target gear, for example, a first speed gear, while the current gear is retained as it is. As shown in FIG. 15B, immediately thereafter, a shift withdrawal of a previous gear (here, the fourth speed gear) is performed during the proceeding of the synchronization of the target gear. A description will be given by referring to a trace shown by the double dotted chain line. In this shift withdrawal, first, it is necessary to smoothly conduct a step (1) for deviating in a select direction from a position of the target gear (first speed gear), a shift step (2) for returning to a neutral line N, a select step (3) for moving to a gear (fourth speed gear), a shift step (4) for moving to the gear (fourth speed gear), a select step (5) for moving into the gear (fourth speed gear) and a shift withdrawal step (6) for moving to the neutral line N (indicated by the double dotted chain line) of the gear (fourth speed gear).
In addition, JP-A-2001-304411 has proposed a shift operation device including a pair of pawl portions provided on each of the shift lugs. Since an interval between the pawl portions is widened in a shift direction, a shift member is allowed to merely move in a select direction from a space between the pair of pawl portions on a shift lug which is in a shifted state so as to be placed between the pair of pawl portions on the shift lug of a target gear in a neutral state, thereby simplifying the movement of the shift member.
As described above, in the dual clutch-type automatic transmission, it is necessary to shift a target gear and perform a shift withdrawal of a current gear in this order at the time of gearshift. Therefore, the movement of the control finger 140 is complicated which results in a prolonged gearshift time.
In particular, in the technique disclosed in JP-A-2001-304411, for the purpose of solving the complicated movement of the control finger 140, the shift member (control finger) can be placed into a space between a pair of pawl portions when the shift member moves in a select direction even in a state that a shift rail of any gear is shifted. For this reason, the pair of pawl portions must be arranged, with an interval between them opened relatively widely. Then, a problem is posed that a wider interval as described above will result in a poor load transmitting efficiency. For example, as shown in FIG. 13, it is necessary that an interval between a pair of pawl portions 121 is set greater as shown in a state of L1 indicated by the solid line than a state of L1′ indicated by the double dotted chain line. Consequently, the pawl portions 121 are pressed by the shift member 140 in a state greatly inclined toward the shift direction.
In this case, where a force of the pawl portions 121 acting on a wall surface by a rotating torque T of a control shaft 100 is given as a tangential force F, a distance from a contact point a of the shift member 140 with the pawl portions 121 to a shaft center C of the control shaft 100 is given as a distance L2 and an inclined angle of a line connecting the contact point a with the shaft center C in a shift direction is given as an angle α, a component force of the tangential force F in the shift direction, that is, a component force P1 which allows the wall surface of the pawl portion 121 to move in the shift direction, or an orthogonal direction, can be obtained by the following formula (1).P1=F*COS α=T*COS α/L2  (1)
In the above formula (1), on the assumption that the distance L2 is constant irrespective of the angle α, it is apparent that the component force P1 is decreased with an increase in the angle α in a range of 0 to 90 degrees. Therefore, as disclosed in JP-A-2001-304411, a larger interval L1 between the pair of pawl portions 121 will decrease the force P1 pressing the wall surface of the pawl portion 121 toward the shift direction, that is, an orthogonal direction, thereby it is necessary to make greater the force P1 pressing toward the shift direction in shifting operation than in a shift withdrawal operation. However, it is difficult to move the shift lug 129 in the shift direction at a higher transmission efficiency, and a larger driving source (for example, an electric motor) is needed for outputting an operation force required due to a decreased transmission efficiency of the operation force, which will result in a larger-sized device and the loss of energy. Alternatively, a greater operation force requires a reduction gear greater in reduction ratio and prolongs the time of moving the shift member accordingly. This poses a problem in reducing the gearshift time.